Laboratory surveillance of influenza-like illness in seven teaching hospitals, South Korea: 2011-2012 season.

Background: A well-constructed and properly operating influenza surveillance scheme is essential for public health. This study was conducted to evaluate the distribution of respiratory viruses in patients with influenza-like illness (ILI) through the first teaching hospital-based surveillance scheme for ILI in South Korea.
Methods: Respiratory specimens were obtained from adult patients (≥18 years) who visited the emergency department (ED) with ILI from week 40, 2011 to week 22, 2012. Multiplex PCR was performed to detect respiratory viruses: influenza virus, adenovirus, coronavirus, respiratory syncytial virus, rhinovirus, human metapneumovirus, parainfluenza virus, bocavirus, and enterovirus.
Results: Among 1,983 patients who visited the ED with ILI, 811 (40.9%) were male. The median age of patients was 43 years. Influenza vaccination rate was 21.7% (430/1,983) during the 2011-2012 season. At least one comorbidity was found in 18% of patients. The positive rate of respiratory viruses was 52.1% (1,033/1,983) and the total number of detected viruses was 1,100. Influenza A virus was the dominant agent (677, 61.5%) in all age groups. The prevalence of human metapneumovirus was higher in patients more than 50 years old, while adenovirus was detected only in younger adults. In 58 (5.6%) cases, two or more respiratory viruses were detected. The co-incidence case was identified more frequently in patients with hematologic malignancy or organ transplantation recipients, however it was not related to clinical outcomes.
Conclusion: This study is valuable as the first extensive laboratory surveillance of the epidemiology of respiratory viruses in ILI patients through a teaching hospital-based influenza surveillance system in South Korea.